Device and a method for applying an even, thin fluid layer to substrates

ABSTRACT

A device for applying an even, thin fluid layer, in particular a phosphoric acid layer, onto substrates, in particular silicon cells for photovoltaic application, is provided with a process chamber, which is provided with a fluid pan and a high-frequency ultrasound device that converts the fluid into fluid mist, and with a transport device that is arranged beneath a fluid-mist dropping shaft of the process chamber for the substrates. To create a device of this type, which permits an application of the fluid onto the silicon cells in question that is substantially more homogeneous regarding both surface area and volume, the fluid-mist dropping shaft of the process chamber tapers in its interior cross-section towards the transport device and discharges into a passage shaft arrangement for the substrates that covers the transport device, and the interior cross-section of the orifice end of the fluid-mist dropping shaft and of the passage shaft arrangement are coordinated with each other, preferably being essentially identical.

The present invention relates to a device for applying an even, thinfluid layer, in particular a phosphoric acid layer, to substrates, inparticular silicon cells for photovoltaic application, in accordancewith the preambles of Claim 1 and of Claim 14, as well as a method forapplying an even, thin fluid layer, in particular a phosphoric acidlayer, to substrates, in particular silicon cells for photovoltaicapplication, in accordance with the preamble of Claim 18.

To be able to manufacture photovoltaic cells made of silicon, aphosphorus doping of the unfinished cells is first necessary. In thefirst step, the cell is wetted using phosphoric acid, and the wettedcells are placed in a high-temperature oven at ca. 800° to 900° C.,where the phosphorus diffuses from the dried acid into the siliconsubstrate. The coating is designed to be very even to achieve equaldistribution in the diffusion process, and it is also designed to bevery economical since the excess phosphoric acid melts onto the cell as“phosphorus glass,” and it can only be removed using hydrofluoric acid,which is accomplished with difficulty.

Phosphoric acid is usually applied to the silicon substrates in such away that the phosphoric acid is atomized by a high-frequency ultrasounddevice, and the phosphoric acid mist is deposited onto the siliconsubstrates. The phosphoric acid mist is conveyed from the processchamber into a dropping shaft, which is relatively wide and is arrangedat a relatively large distance above the silicon substrates, i.e.,cells, that are conveyed past it. One disadvantage in this known devicelies in the fact that it offers no guarantee that the mist will behomogenized, because even light air currents are sufficient to “blow”the mist. In addition, the configuration of the process chamber leads todamaging condensate drops falling onto the silicon cells, which worksagainst achieving a homogeneous wetting or coating result. The attempthas been made to catch condensate drops of this type using a drip panbeneath the dropping shaft, which however has the effect of preventingthe mist even more from being evenly spread.

The objective of the present invention is therefore to create a devicefor applying an even, thin fluid layer, in particular a phosphoric acidlayer, onto substrates, in particular silicon cells for photovoltaicapplication of the aforementioned type, which permits an application offluid, in particular phosphoric acid, onto the substrates in question,in particular the silicon cells, that is substantially more homogeneouswith respect to both surface area and volume.

The features indicated in Claim 1 are provided to achieve this objectivein a device for applying an even, thin fluid layer, in particular aphosphoric acid layer, onto substrates, in particular silicon cells forphotovoltaic application of the aforementioned type.

The measures proposed according to the invention achieve, within anessentially closed circulation system, both homogeneous mist creation aswell as a homogeneous conveying of the fluid mist from the productionlocation (process chamber) to the application location, as well asduring the application to the substrates, in particular silicon cells.This homogeneity relates to deposition on the silicon substrates interms of both surface area and quantity. In addition, the fluid mist iscompressed and additionally homogenized due to the tapering of thefluid-mist dropping shaft and the resulting backing up of the mist.

The features according to Claim 2 indicate a design of the droppingshaft that is simple from the point of view of manufacturing technique.

The features according to Claim 3 indicate that the cover of the passageshaft arrangement disposed above the silicon substrates, which arepassing by, is maintained at a certain temperature, so that the fluidmist cannot condense and thus drop formation is not possible, which alsopromotes the homogeneity of the fluid mist and of its application.

On the basis of the features according to Claim 4 and/or 5, aregulatable, homogeneous, and active conveyance of the fluid mist isachieved from the point of origin to the point of application, as wellas during the application phase. In this context, when the exhaust airduct is used, it is expedient to provide the features according to Claim6 so as to not impair the homogeneity of the fluid mist at the passageend of the shaft arrangement and to impart to the fluid mist a definedflow velocity.

The features according to Claim 7, in a preferred and advantageousmanner, provide that the fluid mist is deposited evenly and insufficient quantity on the silicon substrates due to the gravity thatacts upon the fluid mist and the duration of the reaction time extendingbeyond the time needed for transport.

According to the features of Claim 8, in the area where the fluid mistis produced, an impact element is provided, which has the advantage thatits plastic web catches the fluid without spatter and causes it to flowback into the fluid pan. An advantageous configuration for this purposecan be derived from the features according to Claim 9.

According to the features of Claim 10, a configuration of the cover ofthe process chamber has the advantage, regarding the homogeneity of thefluid mist, that the condensate that collects there can be conveyed backto the fluid pan due to the tilted arrangement.

Correspondingly, in accordance with Claim 11, measures are provided inthe fluid-mist dropping shaft that are capable of removing thecondensate that forms on the walls of the dropping shaft withoutpermitting drops to form. For this purpose, it is expedient to providethe features according to Claim 12, so that the condensate can bedrained off to the side via the channels.

A further preferred design configuration can be derived from thefeatures of Claim 13, having the advantage that the width of a device ofthis type can be extended to a virtually unrestricted degree.

In the known device cited above, a high-frequency ultrasound device isused whose high-frequency ultrasound transmitter, or generator, is notresistant to phosphoric acid. Therefore, it is necessary to use anintermediate receptacle that is filled with water, evacuated, andconnected to a tempering circuit. The high-frequency ultrasoundgenerator is attached on the lower side of the intermediate receptacle,and a diaphragm is attached on the upper side of the intermediatereceptacle, whereby the water and the diaphragm function to transfer thesound from the high-frequency ultrasound transmitter to the phosphoricacid basin or pan, situated above it. Disadvantageous in this respectare the cumbersome and expensive technology, the frequent ruptures ofthe diaphragm due to fatigue, the resulting laborious and time-consumingprocess of replacing the diaphragm, and the damping characteristics of asound transfer means of this type.

To avoid these disadvantages, the features indicated in Claim 14 areprovided in a device of the aforementioned type.

As a result of the measures according to the present invention, both thephosphoric acid and the sound are focused in the quartz glass nozzle. Itis expedient to provide the features in accordance with Claim 15 so thatthe fluid that is compressed in the quartz glass nozzle can flow backthrough the supply lines.

One preferred design configuration in this regard is indicated by thefeatures according to Claim 16.

The features according to Claim 17 enable the high-frequency ultrasounddevice to be in essence directly connected to the phosphoric acidwithout resulting in disadvantages regarding the intensity of thehigh-frequency ultrasound generation.

Furthermore, the present invention relates to a method for applying aneven, thin fluid layer, in particular a phosphoric acid layer, ontosubstrates, in particular silicon cells for photovoltaic application, inaccordance with the preamble of Claim 18.

As previously mentioned, the heretofore comparable methods demonstrate alack of homogeneity in the conveying of the fluid mist and therefore inthe depositing of the phosphoric acid.

To improve this aspect of a method of the aforementioned type, thefeatures indicated in Claim 18 are provided.

On the basis of the measures according to the invention, the fluid mistcan be actively and homogeneously conveyed from the point of generationof the fluid mist to the point of application, or deposition, of thefluid-mist layer onto the substrates.

Advantageous embodiments in this regard are indicated by the featuresaccording to Claim 19 and/or 20.

Further details of the present invention can be derived from thefollowing description, in which the invention is described and discussedin greater detail on the basis of the exemplary embodiment depicted inthe drawing.

In the drawing:

FIG. 1 in a schematic and partial longitudinal cutaway side view,depicts a device for applying an even, thin phosphoric acid layer ontosilicon substrates for photovoltaic application, and

FIG. 2 depicts a high-frequency ultrasound device that is used in thedevice according to FIG. 1 in the installed state and in cross-section.

Device 10 as depicted in FIG. 1 functions to apply an even, thinphosphoric acid layer to silicon substrates, or cells, 12 forphotovoltaic application. In this context, silicon substrates 12 aretransported in and out on a transport device 13 in the direction ofarrow A, and during the transport motion become homogenous with respectto a phosphoric acid layer as a result of the fact that siliconsubstrates 12 are conveyed through a phosphoric acid mist 15 which isgenerated by a high-frequency ultrasound device 11 within a processchamber 14.

According to FIG. 1, a pan 16 containing phosphoric acid is arranged onthe base of process chamber 14 that extends over a defined lengthperpendicular to the plane of the drawing. Phosphoric-acid pan 16 isconnected via a tubular line 18 to a phosphoric-acid tank 19.Advantageously, the phosphoric acid from this tank 19 in pan 16 istempered as needed. High-frequency ultrasound device 11, which isdescribed below in greater detail on the basis of FIG. 2, is attached onbase 21 of fluid pan 16.

In accordance with FIG. 1, process chamber 14 is bordered by a rightsidewall 22, an opposite left sidewall 23, a cover 24, and undepictedend walls that are parallel to the plane of the drawing. Process chamber14, which is situated above fluid tank 19, is provided in its areafacing left sidewall 23 with a dropping shaft 25 that points towardstransport device 13. Cover 24 of process chamber 14 is arranged so as todiagonally slope from right sidewall 23, and it is sealingly joined toleft sidewall 23, which in its extension 23′ that points towardstransport device 13 forms the sidewall of dropping shaft 25. Thissidewall 23, 23′ is tilted diagonally towards transport device 13 in thedirection of right sidewall 22, so that a dropping shaft 25 results thattapers, i.e., is roughly wedge-shaped, whose opposite side wall 26extends vertically and therefore parallel to right sidewall 22 ofprocess chamber 14, which is located higher up. This sidewall 26 ofdropping shaft 25 borders fluid pan 16 and extends beyond fluid surface20 of fluid pan 16, creating a dam 27.

In the upper area of right sidewall 22 of process chamber 14, an impactelement 27 is attached, which, sloping diagonally downwards, i.e.,towards fluid pan 16, protrudes into process chamber 14 and terminatesat a distance before dam 27, creating a passage 29.

Impact element 28 has a frame that is covered with plastic web 30,whereby plastic web 30 in a spatter-free manner catches the phosphoricacid droplets within phosphoric acid mist 15 that are hurled byhigh-frequency ultrasound device 11, and it causes the droplets to flowback into fluid pan 16. Thus only the phosphoric acid mist goes throughpassage 29 and plastic web 30 of impact element 28 into the space ofprocess chamber 14 situated behind them. Plastic web 30 of impactelement 28 also permits the condensate that collects on cover 24 ofprocess chamber 14 and that flows back towards right sidewall 22 to passthrough and flow off into fluid pan 16.

In the area between fluid surface 20 of pan 16 and impact element 28, anair supply connector 31 is provided, whose supply line is furnished witha regulating device 32. In this way, the phosphoric mist that isproduced is pushed, i.e., actively moved through regulatable air supplyline 31, 32, and over dam 27 towards the intake of dropping shaft 25.

Both the parts of left sidewall 23, 23′, which pass into each other, aswell as sidewall 26 of dropping shaft 25 are provided with a webcovering 34, so that the condensate of phosphoric acid mist 15 that isdeposited on the walls of dropping shaft 25 can be conducted away fromthis web covering 34 towards the bottom without the formation of drops.For this purpose, the lower edges of sidewalls 23, 23′, and 26 terminateabove channels 36 and 37, which drain the condensate off to the side ina manner that is not depicted in detail, i.e., in a direction that isperpendicular to the plane of the drawing.

Above transport device 13, i.e., upper side 39 of transport device 13,on which silicon substrates 12 lie and are moved in the direction ofarrow A, a passage shaft arrangement 40 is provided which has an intakearea 41 upstream of dropping shaft 25 and an outlet area 42 downstreamof dropping shaft 25. Between intake area 41 and outlet area 42, shaftarrangement 40 is open on the top, dropping shaft 25 discharging intothis open area. At the rear end in the direction of passage A, outletarea 42 of shaft arrangement 40 is provided with an extraction box 43,within whose opening, which is facing side 39 of transport device 13, aroof-shaped plastic web 45 is arranged so as to create a laminar flowbox. At this end of extractor box 43, facing away from this plastic web45, an extractor line 46 is attached, in which a regulating device 47 isarranged that has a suction fan 48 for actively moving phosphoric acidmist 15, i.e., causing it to flow. Behind suction fan 48 a condensatereturn line 49 is provided which discharges into phosphoric acid tank19.

Based on both regulating devices 32 and 47 for supplying and removingair, phosphoric acid mist 15, once produced, can be moved in regulatablefashion from its production location, namely process chamber 14, viadropping shaft 25, which extends below process chamber 14 and fluid pan16, into shaft arrangement 42 and finally to the location at whichsilicon substrates 12 are to be coated. Due to the wedge-shapedconfiguration of dropping shaft 25, the phosphoric acid mist iscompressed by the backup and is homogenized. Because of the directtransition from dropping shaft 25 to relatively low shaft arrangement40, phosphorus mist 15 remains homogeneous and compressed and thereforecompletely fills outlet area 42 of shaft arrangement 40. Becauseextraction box 43 uniformly suctions off the portion of phosphoric acidmist 15 that was not deposited from the entire width of outlet area 42of shaft arrangement 40, the homogeneity of the phosphoric acid mist ismaintained within outlet area 42. Therefore, due to the gravity actingupon the phosphoric acid mist and the duration of the reaction timeextending beyond the time needed for transport, the phosphoric acid isdeposited on substrates 12 evenly and in sufficient volume. Thephosphoric acid mist is dosed in a sensitive manner by regulating thesupply and removal of air as well as by regulating the power supplied tohigh-frequency ultrasound device 11. A homogeneous and (in time andspace) even action of the phosphoric acid mist on silicon substrates 12is also achieved due to the fact that the transport velocity oftransport device 13 for silicon substrates 12 is coordinated with thevelocity of the phosphoric acid mist 15 as it moves through thesubstantially closed circulation system from process chamber 14 viadropping shaft 25 and shaft arrangement 42 to extraction box 43, and theformer is advantageously synchronized with the latter, i.e., is equal toit.

For an evenly homogeneous conveyance of phosphoric acid mist 15 over theentire path, it is important that the dimensioning or, in other words,the discharge end, of vertical fluid-mist dropping shaft 25 and ofpassage shaft arrangement 40 bordering the deposition chamber forsubstrates 12 are coordinated with each other, and preferably areidentical.

In order to prevent condensate of phosphoric acid mist 15 from formingon cover 51 of shaft arrangement 40 beneath outlet area 42 of shaftarrangement 40, a return shaft 52 whose base is formed by cover 51 isprovided above outlet area 42. Return shaft 52 is connected by a line 53to a filling level tube 54 of phosphoric acid pan 16 in an area of theentry end of outlet area 42 of shaft arrangement 40, so that temperedphosphoric acid that overflows from pan 16 can flow over shaftarrangement 40 in transport direction A. At the end of return shaft 52behind a dam-like element 56, a tubular line 57 is connected whichreturns the excess phosphoric acid to phosphoric acid tank 19.

FIG. 2 in a detail of FIG. 1 depicts high-frequency ultrasound device 11that is used in device 10, shown in a schematic longitudinal cutawayview. High-frequency ultrasound device 11 has a plastic housing 61,which penetrates a borehole 62 in base 21 of the phosphoric acid pan andis attached by a flange of 63 to the lower side of pan base 21. Within alower hollow housing part 64 that is surrounded by flange 63, apiezoelectric element 65 is arranged which is located in the area of panbase 21 as the high-frequency ultrasound generator, whose lower side isprovided in an undepicted manner with connecting lines and whose upperside is filled by and preferably glued to a quartz glass disk 66. Thethickness of quartz glass disk 66 is coordinated with the high-frequencyultrasound frequency of piezoelectric element 65, so that the sound canbe relayed virtually without loss. This unit, composed of piezoelectricelement 65 and quartz glass disk 66, is installed in hollow housing part64 so as to be hermetically sealed towards the lower side, the quartzglass disk being arranged first on the side facing the phosphoric acidin pan 16. A quartz glass nozzle 68 at its lower, larger-diameter end isscrewed into upper hollow housing part 67, which constitutes an integralpiece with hollow housing part 64 and protrudes into phosphoric acid pan16. A multiplicity of radial bore holes 69 arranged around thecircumference are introduced into upper hollow housing part 67, throughwhich the phosphoric acid contained in pan 16 can flow into the space ofquartz glass nozzle 68 and also come into contact with quartz glass disk66. Quartz glass nozzle 68 tapers to an orifice 71 protruding intoprocess chamber 14. Therefore the tip of quartz glass nozzle 68, whichis provided with orifice 71, protrudes somewhat beyond fluid surface 20of the phosphoric acid in pan 16. Both the phosphoric acid and the soundare focused in quartz glass nozzle 68 if, due to the high-frequencyultrasound energy of piezoelectric element 65, the phosphoric acid thatis contained in nozzle 68 is spattered via disk 66 beyond fluid surface20 of the phosphoric acid in pan 16. A pronounced buildup of phosphoricacid mist 15 is generated in the area around the spattered phosphoricacid. As mentioned, the phosphoric acid droplets, which separate fromthe phosphoric acid mist on the impact element, are caught by pan 16.

The phosphoric acid that is compressed in quartz glass nozzle 68 so asto form the phosphoric acid mist 15 can flow out of pan 16 via radialboreholes 69.

It should be noted that device 10 depicted in FIG. 1 may also beequipped with a high-frequency ultrasound device that is configured in adifferent manner in place of high-frequency ultrasound device 11 inaccordance with FIG. 2.

1-20. (canceled)
 21. A device for applying an even, thin fluid layer, inparticular a phosphoric acid layer, onto substrates, in particularsilicon cells for photovoltaic application, including: a processchamber, provided with a fluid pan, a fluid-mist dropping shaft, and ahigh-frequency ultrasound device that converts the fluid into fluidmist; a passage shaft arrangement for the substrate; and a transportdevice that is arranged beneath said fluid-mist dropping shaft of saidprocess chamber for the substrates, wherein: said fluid-mist droppingshaft of said process chamber tapers in its interior cross-sectiontowards said transport device and discharges into said passage shaftarrangement for the substrates that covers said transport device, andthe interior cross-section of the orifice end of said fluid-mistdropping shaft and of said passage shaft arrangement are coordinatedwith each other, preferably being essentially identical.
 22. The deviceas recited in claim 21, wherein: said fluid-mist dropping shaft iswedge-shaped in the direction of said passage shaft arrangement.
 23. Thedevice as recited in claim 21, wherein: said passage shaft arrangementin the passage direction downstream of the orifice of said droppingshaft a return shaft is arranged that is connected to said fluid pan,the rear end of the return shaft that faces away from the orifice beingconnected to a fluid tank.
 24. The device as recited in claim 21,wherein: in an area above said high-frequency ultrasound device an airsupply pipe discharges that is connected to a first regulating device.25. The device as recited in claim 24, wherein: at the end of saidpassage shaft arrangement an air discharge channel is provided that isconnected to a second regulating device.
 26. The device as recited inclaim 25, wherein: between said passage shaft arrangement and said airdischarge channel an extractor, box is arranged that is provided with alaminar flow box that is connected to a suction fan.
 27. The device asrecited in claim 25, wherein: said first and said second regulatingdevice can be coordinated with each other, preferably synchronized, forthe velocity of the mist as it moves from said process chamber throughsaid passage shaft arrangement and the velocity of said transport devicefor the substrates.
 28. The device as recited in claim 21, wherein: animpact element that has a web, preferably a plastic web, is providedwithin said process chamber above said high-frequency ultrasound deviceand said fluid pan.
 29. The device as recited in claim 28, wherein: apassage for the fluid mist is provided between the free end of a tiltedimpact element, which emerges from a process chamber wall that facesaway from said dropping shaft and a dam that is arranged on the end ofsaid fluid pan that faces away from said process chamber wall.
 30. Thedevice as recited in claim 21, wherein: a cover of said process chamberis tilted at a rising slope as it emerges from the process chamber wallthat faces away from said dropping shaft.
 31. The device as recited inclaim 21, wherein: said wedge-shaped fluid-mist dropping shaft on itsbordering walls is furnished with a web covering.
 32. The device asrecited in claim 31, wherein: said bordering walls of said droppingshaft terminate in the orifice area of said passage shaft arrangementvia runoff channels.
 33. The device as recited in claim 21, wherein: inaccordance with a width of said transport device transverse to thepassage direction and therefore of said process chamber, a multiplicityof high-frequency ultrasound devices are provided at pre-establishedintervals in this direction.
 34. The device for applying an even, thinfluid layer, in particular a phosphoric acid layer, onto substrates, inparticular silicon cells for photovoltaic application, including aprocess chamber, provided with a fluid pan and a high-frequencyultrasound device that converts the fluid into fluid mist, as recited inclaim 21 wherein: said high-frequency ultrasound device for atomizingthe fluid is provided with a nozzle, preferably made of quartz glass,beneath which a high-frequency ultrasound generator is arranged.
 35. Thedevice as recited in claim 34, wherein: supply lines are providedbetween said nozzle that protrudes from the fluid surface in said fluidpan and a high-frequency ultrasound generator to allow the fluid to flowfrom said pan into the nozzle.
 36. The device as recited in claim 34,wherein: said nozzle is held in a housing, preferably made of plastic,which is secured on the base of the fluid pan and penetrates this basein a fluid-tight manner, the high-frequency ultrasound generator isattached in said housing in the area of said pan base, and a multitudeof radial supply boreholes are provided in the part of the housing thatis located within said fluid pan.
 37. The device as recited in claims34, wherein: said high-frequency ultrasound generator is a piezoelectricelement, on which a quartz glass plate is attached, preferably glued,which faces said nozzle and is coordinated with the ultrasoundfrequency.
 38. A method for applying an even, thin fluid layer, inparticular a phosphoric acid layer, onto substrates, in particularsilicon cells for photovoltaic application, comprising the steps of:generating a fluid mist within a process chamber, which settles, i.e.,is deposited, on substrates that are preferably moved by a transportdevice; actively moving the fluid mist out of the process chamber on itsway to the substrates; comprising and homogenizing in a dropping shaftthat is connected to the process chamber the fluid mist; and conveyingthe fluid mist from there into a passage shaft arrangement that isarranged over the moving substrates, and is deposited upon thesubstrates, whereby the active process of moving the fluid mist iscoordinated with the velocity of the substrates, preferably beingsynchronized therewith.
 39. The method as recited in claim 38, wherein:fluid is directly returned that has been heated on the passage shaftarrangement that conveys the fluid mist to be deposited.
 40. The methodas recited in claim 38, wherein: the fluid mist is evenly suctioned offas residue at the end of the passage shaft arrangement.